A common type of printer causes impact members such as print hammers or print wires to impact against a record medium that is moved past a printing line. The movement of the print hammers or print wires is typically caused by an electromagnetic system employing solenoids, which system enables precise control of the impact members.
In the field of dot matrix printers, it has been quite common to provide a printhead which has included therein a plurality of print wire actuators or solenoids arranged or grouped in a manner to drive the respective print wires a very short, precise distance from a reset or non-printing position to an impact or printing position. The print wires are generally either secured to or engaged by the solenoid plunger or armature which is caused to be moved such precise distance when the solenoid coil is energized. The plunger or armature normally operates against the action of a return spring.
It has also been quite common to provide an arrangement or grouping of such solenoids in a circular configuration to take advantage of reduced space available in the manner of locating the print wires in that area between the solenoids and the front tip of the printhead adjacent the record media. In this respect, the actuating ends of the print wires are positioned in accordance with the circular arrangement and the operating or working ends of the print wires are closely spaced in aligned manner adjacent to the record media. The availability of narrow or compact actuators permits a narrower or smaller printhead to be used and thereby reduces the width of the printer because of the reduced clearance at the ends of the print line. The printhead can also be made shorter because the narrow actuators can be placed in side-by-side manner closer to the record media for a given amount of wire curvature.
State-of-the-art circuitry commonly uses analog circuits to control dot matrix printhead energy. Usually individual solenoid current or applied printhead voltage is sensed and fed back into an analog control circuit to maintain proper printhead impact energy by varying pulse duration to compensate for voltage changes. Such analog circuits are not normally amenable to large scale integration techniques such as are used with digital type circuits commonly found in a microprocessor environment. Use of diital circuitry to perform the control functions commonly performed by analog circuitry in dot matrix printers would be advantageous in permitting the combination of such control circuitry with other digital circuitry associated with microprocessors in large scale integration.